The code provided models the concept of volume transmission within the brain, specifically focusing on neuromodulation. Volume transmission refers to the diffusion of neurotransmitters and neuromodulators across extracellular space, influencing a large number of neurons over a broad area. This is in contrast to synaptic or wiring transmission, where neurotransmitters are released in the synaptic cleft and affect neurons in a more direct and localized manner. ### Biological Basis 1. **Neuromodulators**: Neuromodulators like dopamine, serotonin, and norepinephrine are chemicals in the brain that modulate the neuron's responses to other neurotransmitters. Unlike classical neurotransmitters, they are often released at sites away from synapses and diffuse through tissue to reach their targets, engaging in volume transmission. 2. **Volume Transmission**: The concept of volume transmission allows signal molecules to influence multiple neurons that might not be synaptically connected. This broad signaling mechanism plays a critical role in the regulation of mood, arousal, attention, and learning. In the brain, the release of these modulatory substances can affect entire networks, thereby adjusting the body's responses to various stimuli. 3. **Temporal Dynamics**: The `deliver_interval_` parameter in the code reflects the timing aspect of neuromodulatory signaling. In biological terms, this could represent the frequency or periodicity with which neuromodulatory signals are assessed or delivered across the network. It implies that the model captures not just the diffusion dynamics, but also the temporal patterns of neuromodulator action. 4. **Spike Events and Multiplicity**: The code handles spike events and registers the multiplicity of these events, which in biological terms corresponds to the frequency or strength of neuromodulator release. This is important because the multiplicity can affect the overall concentration of neuromodulators in the extracellular space and hence their impact. 5. **Dopamine as a Model Neuromodulator**: The code specifically refers to `dopamine spike` as a pseudo event. Dopamine is a key neuromodulator involved in reward processing, motor control, and the regulation of mood. This suggests that the volume_transmitter is modeling the network effects of dopamine through volume transmission. 6. **Distribution Across Targets**: The method `register_connector` suggests the presence of a set of target neurons or synapses influenced by the neuromodulatory signals. In biology, this means that neuromodulators released in one region can spread and interact with multiple targets simultaneously, affecting their synaptic strength or plasticity. Overall, the code is an abstraction of the biological mechanism by which neuromodulators are released, diffuse through the brain, and modulate neural network activity on a larger scale than synaptic transmission alone. This abstraction allows for computational models that capture the integrative and regulatory roles of neuromodulators in complex neural processes.